The Centre for Health Protection (CHP) of the Department of Health is tonight (September 19) investigating a local case of dengue fever (DF), and again urged the public to maintain strict environmental hygiene, mosquito control and personal protective measures both locally and during travel.

The female patient, aged 59 with good past health, has developed fever, chills and skin rash since September 9. She was afebrile upon admission to Queen Mary Hospital on September 15 for management and has been discharged today in stable condition all along.

Initial enquiries revealed that the patient lives in Tin Ma Court, Wong Tai Sin, and had no recent travel history. During the incubation period, according to the patient, she mainly stayed at home and went to her workplace on Argyle Street, Kowloon City. Further investigations into her local movements are underway.

Her home contacts have remained asymptomatic so far and have been put under medical surveillance.

"The CHP immediately commenced epidemiological investigations and promptly informed the Food and Environmental Hygiene Department (FEHD) for vector investigation and mosquito control. Investigations and health education in vicinities where the patient frequented are proceeding," a spokesman for the CHP said.

Officers of the CHP will conduct site visit and field investigations by questionnaire surveys at the patient's residence for active case finding and arranging blood tests.

"Further to the three local cases earlier, we are conducting extensive investigations with the FEHD to control the possible spread," a spokesman for the CHP said.

Four local cases have been detected to date in 2016. While epidemiological investigations into the first three local cases are ongoing, persons who have been to the vicinity of Central or Mid-Levels, or Tin Ma Court, Wong Tai Sin with DF symptoms should call the CHP's hotline (2125 2266) for laboratory investigation or referral as appropriate. No abnormalities have been identified so far.

Members of the public should:

Inspect the household or workplace to check for potential mosquito breeding sites and remove them. Leave no stagnant water;

Apply DEET-containing insect repellents to exposed parts of the body and clothing; and

"We will issue letters to doctors and hospitals to alert them to the case. We will also enhance surveillance of suspected cases in collaboration with public and private hospitals as well as private doctors. Early referral and prompt control are critical to prevent further local spread," the spokesman said.

Dengue viruses encompass four serotypes, each of which can lead to DF and severe dengue (dengue haemorrhagic fever). Symptoms of first infection are usually mild. Once recovered, immunity to that serotype will develop, but subsequent infections of other serotypes are more likely to result in severe dengue, which is potentially fatal.

DF is transmitted to humans by bites of infective Aedes mosquitoes. When a dengue patient is bitten by a mosquito, it is infected and may spread the disease by biting others. In Hong Kong, the principal vector, Aedes aegypti, is not found, but the prevailing species, Aedes albopictus, can also spread the disease.

There is no locally registered dengue vaccine in Hong Kong. Eliminating stagnant water as breeding sites for mosquitoes and avoiding mosquito bites are key to preventing DF.

Apart from general measures, travellers returning from affected areas should apply insect repellent for 14 days upon arrival in Hong Kong. If feeling unwell, seek medical advice promptly and provide travel details to the doctor.